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Co-authored-by: str4d <[email protected]>

zcash_client_backend/src/data_api/chain.rs

@@ -53,7 +53,7 @@
 use zcash_primitives::{
     consensus::{self, BlockHeight},
     sapling::{self, note_encryption::PreparedIncomingViewingKey},
-    zip32::Scope,
+    zip32::Scope, block::BlockHash,
 };
 
 use crate::{
@@ -197,6 +197,16 @@ where
             if let Some(scan_error) = check_continuity(&block, continuity_check_metadata.as_ref()) {
                 return Err(Error::Scan(scan_error));
             }
+
+            if from_height == BlockHeight::from(0) {
+                // We can always derive a valid `continuity_check_metadata` for the
+                // genesis block, even if the block source doesn't have
+                // `sapling_commitment_tree_size`. So briefly set it to a dummy value that
+                // ensures the `map` below produces the correct genesis block value.
+                assert!(continuity_check_metadata.is_none());
+                continuity_check_metadata =
+                    Some(BlockMetadata::from_parts(BlockHeight::from(0), BlockHash([0; 32]), 0));
+            }
             continuity_check_metadata = continuity_check_metadata.as_ref().map(|m| {
                 BlockMetadata::from_parts(
                     block.height(),

zcash_client_backend/src/scanning.rs

@@ -153,7 +153,7 @@ impl fmt::Display for ScanError {
                 write!(f, "Block height discontinuity at height {}; next height is : {}", prev_height, new_height)
             }
             ScanError::TreeSizeMismatch { protocol, at_height, given, computed } => {
-                write!(f, "The the {:?} note commitment tree size provided by a compact block did not match the expected size at height {}; given {}, expected {}", protocol, at_height, given, computed)
+                write!(f, "The {:?} note commitment tree size provided by a compact block did not match the expected size at height {}; given {}, expected {}", protocol, at_height, given, computed)
             }
             ScanError::TreeSizeUnknown { protocol, at_height } => {
                 write!(f, "Unable to determine {:?} note commitment tree size at height {}", protocol, at_height)